Intense or out of control, but typically in a good or fascinating way. The term is derived from a boxing metaphor - when boxers train on a heavy bag they can knock the bag "off the hook". Also see "knock him out of the box" for another popular boxing metaphor.

Did you see that Russian climbing video? Damn, those dudes were flipping off four story buildings! It was off the hook!

Free from a difficult situation.
To be in a difficult situation is like hanging "on" a "hook"; to get free of the problem you must get "off the hook".

We've caught you again, but this time you won't get off the hook so easily!" You are "off the hook" when you are no longer responsible for some problematic situation. Example: "We found the guy who stole the money, so we know you didn't do it; you're off the hook." When you get yourself free from a difficult situation you are no longer "on the hook"; you are "off the hook." Example: "You're lucky; it turns out that Dad never heard you come in late last night." Answer: "Great, that means I'm off the hook!

A truly outrageous party or gathering. To recieve this moniker, the experience should of transcended the norm and in fact gone way beyond it - to realms that are (almost) void of defintion. The happiness, love and sheer exuberance of it all should of reminded everyone in attendance the joy of what is to be alive. Off the hook is as close as we've got thus far to describe such an event. Use sparingly.

"How was your weekend Jim?"
"Jesus, fucking Christ, it was insane, completely and utterly off hook!"
"Oh, very well. I need those insurance reports on my desk first thing!"